The invention relates to an angular position sensor unit consisting of an encoder disc that is connected by way of a hub to the element on which a measurement is performed for the purpose of determining the angular position of a shaft, axle or wheel.
To measure angles of rotation and/or numbers of revolutions, one uses angular position sensors that have to meet exacting requirements in regard to the accuracy of the measurement within a wide temperature range. A particular problem exists in the mechanical fixation of the encoder disc on a suitable carrier, e.g., a hub, because the connection between the encoder disc and its carrier needs to be play-free and stress-free in relation to a sensor/emitter unit in the axial and radial directions over the entire specified temperature range.
The object of the present invention is to further develop an angular position sensor of the kind described above, so that a measuring accuracy of xe2x89xa60.5 degrees of angle is achieved within a temperature range of xe2x88x9240 to +80xc2x0 C. and unrestricted functionality is maintained in the presence of vibrations in a frequency range between 8 and 200 Hz with an effective acceleration of  greater than 1 g.
To meet the foregoing objective, the invention provides an angular position sensor unit with an encoder disc, a hub and a retainer. The hub is designed to be connected to an element whose angular position is to be measured. The encoder disc is made of a plastic material with a thickness between 0.1 and 1.0 mm and a planarity of  less than 0.2 mm. An opening through the center of the encoder disc is engaged in a flange of the hub. The flange has three or more ridges extending symmetrically in radial directions and engaging three punched slots of the encoder disc. The slots conform to the contours of the ridges, so that the encoder disc is held in its position relative to the hub in a form-fitting, positive manner. In the axial direction, the disc is locked in place by the retainer.
In practical embodiments of the invention, it has been found advantageous, if the encoder disc and the hub are designed and manufactured substantially in accordance with the following dimensional tolerances:
for the central opening of the encoder disc, +0.1 mm;
for the slot width of the encoder disc, +0.1 mm;
for the slot length of the encoder disc, +0.1 mm;
for the width of the ridges on the hub, xe2x88x920.05 mm; and
for the length of the ridges on the hub, xe2x88x920.05 mm.
Further in accordance with the invention, it has been found practical if the hub and the retainer are arranged on a common axis.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.